Techniques for improving a fiber scanning system

ABSTRACT

A fiber scanning system can have optimized performance by substantially matching the natural frequencies of the fiber scanning system&#39;s actuator and fiber optic scanning element. By matching the natural frequencies, the fiber scanning system can increase the maximum distance that the tip of the fiber optic scanning element may be driven relative to a resting position. Such an effect may be produced because matching the natural frequencies of the fiber scanner allows for larger amplitudes to be achieved. It should be noted that the natural frequency of the scanning system can be selected to avoid excitation frequencies that could destabilize the system. In this way, the system as a whole may act as a tuned mass damper or a tuned resonance structure, thereby improving scan performance while maintaining a stable scanning system.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/471,913, filed on Mar. 15, 2017, entitled “DYNAMIC ABSORBER MODEFIBER SCANNER”, the disclosure of which is hereby incorporated byreference in its entirety for all purposes.

BACKGROUND

An image projector can be an optical device that projects an image (ormoving images) for a user to view. Recently, innovations have allowed ahead-mounted device to include an image projector. Such image projectorscan project images to the eyes of a user wearing the head-mounteddevice. However, image projectors small enough to be used with ahead-mounted device typically project an image with a narrow field ofview. Therefore, there is a need in the art for an improved design foran image projector to use with a head-mounted device.

SUMMARY

Provided are methods, systems, and computer-program products for animproved design of a fiber scanning system. For example, the performanceof the fiber scanning system can be optimized by substantially matchingthe natural frequencies of the fiber scanning system's actuator andfiber optic scanning element. By matching the natural frequencies, thefiber scanning system can increase the maximum distance that the tip ofthe fiber optic scanning element may be driven relative to a restingposition of the fiber optic scanning element. Such an effect may beproduced because matching the natural frequencies of the fiber scannerallows for larger amplitudes to be achieved. It should be noted that thenatural frequency of the scanning system can be selected to avoidexcitation frequencies that could destabilize the system. In this way,the system as a whole may act as a tuned dynamic absorber or a modalenergy transfer optimizer for an oscillator, thereby improving scanperformance while maintaining a stable scanning system.

According to an embodiment of the present invention, a method forincreasing a field of view of a fiber scanning system is provided. Themethod includes configuring a fiber scanning system to behave as a tuneddynamic absorber by selecting (1) an actuator characterized by a firstactuator natural frequency and (2) a fiber optic scanning elementcharacterized by a first fiber natural frequency that is within athreshold of the first actuator natural frequency. Alternatively, themethod includes configuring a fiber scanning system to behave as a tuneddynamic absorber by selecting (1) a fiber optic scanning elementcharacterized by a second fiber natural frequency and (2) an actuatorcharacterized by a second actuator natural frequency that is within athreshold of the second actuator natural frequency. The method alsoincludes driving the fiber scanning system at an operating frequency.

According to another embodiment, a method for increasing a field of viewof a fiber scanning system is provided. The method includes configuringthe fiber scanning system to behave as a tuned dynamic absorber by:providing (1) an actuator characterized by an actuator natural frequencyand (2) a fiber optic scanning element characterized by a fiber naturalfrequency that is within a threshold of the actuator natural frequency.A first displacement gain is associated with operation of the fiberscanning system at the fiber natural frequency. The method also includesdetermining a range of operating frequencies. The range extends from afirst operating frequency less than the fiber natural frequency andassociated with the first displacement gain to a second operatingfrequency greater than the fiber natural frequency and associated withthe first displacement gain. The method further includes driving theactuator at an operating frequency within the range.

In some examples, the fiber scanning system can include an actuator(e.g., a piezoelectric tube) and a fiber optic scanning element. In suchexamples, the fiber scanning system can be optimized such that anactuator natural frequency (of the actuator) can be determined to matcha fiber natural frequency (of the fiber optic scanning element). In thismanner, energy from the actuator can be more efficiently transferred tothe fiber optic scanning element, increasing an overall deflection ofthe fiber optic scanning element, which can provide a wider field ofview for the fiber scanning system.

Numerous benefits are achieved by way of the present disclosure overconventional techniques. For example, embodiments of the presentdisclosure provide an increased deflection of a tip of a fiber opticscanning element for a given energy input, increasing a field of view ofa scanning fiber system.

Provided is a fiber scanning system. For example, a fiber scanningsystem can include an actuator (e.g., a piezoelectric tube)characterized by an actuator natural frequency of operation and a fiberoptic scanning element coupled to the actuator. In some examples, thefiber optic scanning element can be characterized by a fiber naturalfrequency that is determined to match the actuator natural frequency. Inexamples with a piezoelectric tube, the piezoelectric tube can have acylindrical geometry having a central axis, where the fiber opticscanning element passes through the piezoelectric tube along the centralaxis.

In some examples, one or more attributes of the actuator can beconfigured to produce the actuator natural frequency of operation. Insuch examples, an attribute of the one or more attributes can be Young'sModulus, second moment of area, density, area of the cross section,length, or a mode constant.

In some examples, the actuator natural frequency and the fiber naturalfrequency can match within a threshold (e.g., 10 percent). In suchexamples, the actuator natural frequency of operation can characterizethe actuator when the fiber optic scanning element is separate from theactuator.

Also provided is a method for increasing the field of view for a fiberscanning system. For example, the method can include providing anactuator characterized by an actuator natural frequency of operation. Insome examples, the fiber scanning system can include the actuator. Themethod can further include providing a fiber optic scanning element thatcouples to the actuator. In some examples, the fiber optic scanningelement can be characterized by a fiber natural frequency that isdetermined to match the actuator natural frequency. In such examples,the fiber scanning system can further include the fiber optic scanningelement. The method can further include driving the actuator at anoperating frequency.

In some examples, a displacement gain of the fiber scanning system canbe characterized by two split frequency peaks bounding the actuatornatural frequency. In such examples, the operating frequency can be near(i.e., at a frequency within a threshold of) a first peak of thefrequency peaks, where the first peak is less than the actuator naturalfrequency. In other examples, the operating frequency can be near (i.e.,at a frequency within a threshold of) a second peak of the frequencypeaks, where the second peak is more than the actuator naturalfrequency. In other examples, the operating frequency can be near (i.e.at a frequency within a threshold of) the actuator natural frequency. Insome examples, the actuator can be driven by a sinusoidal voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures:

FIG. 1 illustrates an example of a fiber scanning system according to anembodiment of the present disclosure;

FIG. 2 illustrates an example of an image projector using a fiberscanning system according to an embodiment of the present disclosure;

FIG. 3 illustrates an example of a spiral pattern formed by a movingfiber scanning system according to an embodiment of the presentdisclosure;

FIG. 4A illustrates an example of a cross section of a dynamicabsorption design for a fiber scanning system according to an embodimentof the present disclosure;

FIG. 4B illustrates an example of a cross section of an alternativedesign for a fiber scanning system according to an embodiment of thepresent disclosure;

FIG. 4C illustrates an example of a cross section of a fiber scanningsystem indicating a hub and a plate;

FIG. 5A illustrates an example of Bode plots for an alternative designfor a fiber scanning system according to embodiments of the presentdisclosure;

FIG. 5B illustrates an example of Bode plots for a dynamic absorptiondesign for a fiber scanning system according to embodiments of thepresent disclosure;

FIG. 5C illustrates an example of Bode plots for a comparison of adynamic absorption design and an alternative design for a fiber opticscanning element according to embodiments of the present disclosure;

FIG. 5D illustrates an example of Bode plots for a comparison of adynamic absorption design and an alternative design for an actuatoraccording to embodiments of the present disclosure; and

FIG. 6 illustrates an example of a process for increasing the field ofview for a fiber scanning system.

DETAILED DESCRIPTION

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofembodiments of this disclosure. However, it will be apparent thatvarious embodiments may be practiced without these specific details. Thefigures and description are not intended to be restrictive.

The ensuing description provides exemplary embodiments only, and is notintended to limit the scope, applicability, or configuration of thisdisclosure. Rather, the ensuing description of the exemplary embodimentswill provide those skilled in the art with an enabling description forimplementing an exemplary embodiment. For example, while the descriptionmight describe a piezoelectric tube, it should be recognized that anytype of actuator can be used. It should also be understood that variouschanges may be made in the function and arrangement of elements withoutdeparting from the spirit and scope of the disclosure as set forth inthe appended claims.

An image projector can be an optical device that projects an image (ormoving images) for a user to view. In some examples, the image projectorcan project an image in the form of light into one or more eyes of auser. In such examples, the image projector can be in the form of one ormore fiber scanning systems, which can each project light, using a fiberoptic scanning element and an actuator, in various patterns (e.g.,raster scan, spiral scan, Lissahous, or the like) into the one or moreeyes of the user. In addition to projecting light, the fiber scanningsystem can receive emitted light. In particular, the same fiber scanningsystem that projects light may be used to receive light.

FIG. 1 illustrates an example of a fiber scanning system 100 accordingto an embodiment of the present disclosure. The fiber scanning system100 can include an actuator 110 (such as a piezoelectric tube) and afiber optic scanning element 120 (e.g., a single fiber or a multicorefiber optic scanning element). In some examples, the actuator 110 can becoupled to the fiber optic scanning element 120, causing the fiber opticscanning element 120 to be cantilevered. In such examples, the actuator110 may be used to scan (or move) a tip of the fiber optic scanningelement 120 for projecting light to one or more eyes of a user.

FIG. 2 illustrates an example of an image projector using a fiberscanning system 200 according to an embodiment of the presentdisclosure. In some examples, the fiber scanning system 200 can includean actuator 210 (which can correlate with the actuator 110 in FIG. 1)and a fiber optic scanning element 220 (which can correlate with thefiber optic scanning element 120 in FIG. 1). In such examples, the fiberoptic scanning element 220 can be scanned by the actuator 210 to createa set of beamlets with a plurality of angles of incidence and points ofintersection that are relayed to an eye 240 by a waveguide 230. Forexample, a collimated light field image can be injected into thewaveguide 230 to be translated to the eye 240.

FIG. 3 illustrates an example of a spiral pattern formed by a movingfiber scanning system according to an embodiment of the presentdisclosure. In particular, spiral 310 illustrates a multicore fiberoptic scanning element 330 and spiral 320 illustrates a single fiberoptic scanning element 340. In some examples, a constant pattern pitchcan provide for a uniform display resolution. In such examples, a pitchcan be a distance between successive spiral passes along a common vectorfrom an origin of the multicore fiber optic scanning element 330.

FIG. 4A illustrates an example of a cross section of a dynamicabsorption design for a fiber scanning system 400 according to anembodiment of the present disclosure. The fiber scanning system 400 caninclude an actuator 410 (which can correlate with the actuator 110 inFIG. 1). The fiber scanning system 400 can also include a fiber opticscanning element 420 (which can correlate with the fiber optic scanningelement 120 in FIG. 1). As described below, the fiber optic scanningelement 420 can be utilized as a scanning fiber of a fiber scanningdisplay system.

In FIG. 4A, the actuator of the fiber scanning system is implemented asa piezoelectric tube and, for purposes of clarity, the discussion hereinutilizes the term piezoelectric tube, but it will be understood thatembodiments of the present disclosure can utilize actuators other thanpiezoelectric tubes. For example, voice coil actuators, thermalactuators, electrostatic driven actuators, electromagnetic actuators, orthe like can be used. Accordingly, the description of piezoelectrictubes should be understood to include description of the more generalclass of actuators and the present disclosure is not limited toactuators implemented as piezoelectric tubes.

In the example embodiment illustrated in FIG. 4A, the actuator 410 ischaracterized by a cylindrical geometry. In addition, the fiber opticscanning element 420 passes through the actuator 410 along the centralaxis of the fiber optic scanning element 420 and is mechanically coupledto the actuator 410 at a central position 412. Although the fiber opticscanning element 420 is coupled to the actuator 410 at the centralposition 412, i.e., at a radial position of zero radius, this is notrequired by the present disclosure and other coupling positions can beutilized according to embodiments of the present disclosure. Therefore,it should be recognized that the fiber optic scanning element 420 cancouple to other locations of the actuator 410. In some examples, thefiber optic scanning element 420 can couple to the actuator 410 usingepoxy.

In some examples, the fiber scanning system 400 can further include anintermediate element between the fiber optic scanning element 420 andthe actuator 410. In such examples, the intermediate element may be afused silica ferrule or a microfabricated (e.g., fused silica or singlecrystal silicon) joint.

In some examples, an outside diameter of the fiber optic scanningelement 420 at the central position 412 and an inside diameter of theactuator 410 at the central position 412 can be the same. In otherexamples, the diameters can be different (i.e., the outside diameter canbe smaller than the inside diameter. In such examples, a retentioncollar can be used to surround and contact the fiber optic scanningelement 420.

In some examples, the fiber optic scanning element 420 can be coupled tothe actuator 410 using epoxy, filled epoxy (e.g., carbon nanotubes,nanorubbers, graphene, nanosilica additives, or the like), solder glass,solder, any adhesive, or the like.

In some examples, the actuator 410 can have a natural frequency(sometimes referred to as an actuator natural frequency or aneigenfrequency) based on one or more attributes of the actuator 410 (asdescribed below). The actuator natural frequency can be described as afrequency with which the actuator 410 oscillates without external forcesis left to vibrate on its own after an initial disturbance (as describedin Mechanical Vibrations, Third Addition, pg. 53, Rao S. S.,Addison-Wesley Publishing Company, New York 1995). In some examples, theactuator natural frequency is characteristic of the actuator 410separate from the fiber optic scanning element 420.

In some examples, the fiber optic scanning element 420 can also have anatural frequency (sometimes referred to as a fiber natural frequency).The fiber natural frequency (sometimes referred to as a fiber resonancefrequency) can be a frequency at which the fiber optic scanning element420 (independent of or separate from the actuator 410) tends tooscillate in the absence of any driving or damping force. The fibernatural frequency can be the same as or different than the actuatornatural frequency. In some examples, the fiber natural frequency can bemuch less than the actuator natural frequency (as shown in FIG. 4B). Insome examples, the fiber optic scanning element 420 can absorb moreenergy when the frequency of its oscillations matches the actuatornatural frequency.

In some examples, the fiber scanning system 400 can be optimized suchthat the fiber natural frequency can be within a threshold (e.g., 10%)of the actuator natural frequency when the fiber optic scanning element420 is separate or independent from the actuator 410. By matching thenatural frequencies within the threshold, energy from the actuator 410can be more efficiently transferred to the fiber optic scanning element420, gaining a larger overall deflection of the fiber optic scanningelement 420, which can result in a larger (or wider) field of view foran image. The equality between or the matching of the actuator naturalfrequency and the fiber natural frequency can enable efficient energytransfer from the actuator 410 to the fiber optic scanning element 420as described herein. The equality or matching is discussed in relationto a threshold of 10%, but this is not required by the presentdisclosure. In some examples, the threshold is less than 10% (e.g., 5%,2%, 1%, or the like). In other examples, the threshold is greater than10% (e.g., 15%, 20%, or the like). One of ordinary skill in the artwould recognize many variations, modifications, and alternatives.

As mentioned above, the actuator natural frequency can be based on oneor more attributes of the actuator 410. In some examples, the one ormore attributes can be adjusted such that the actuator natural frequencyis determined to match (be within the threshold of) the fiber naturalfrequency. In such examples, the one or more attributes of the actuator410 can include, but is not limited to: Young's Modulus, second momentof area, density, area of the cross section, length, and a modeconstant. The actuator natural frequency can be expressed as:

${f_{n} = {\frac{1}{2\pi}\left( {\beta \; {L(i)}} \right)^{2}\sqrt{\frac{EI}{\rho \; {AL}^{4}}}}},$

where f_(n) can be a natural frequency of the actuator 410, β can be amode constant, L can be a length of the actuator 410, i can be aninteger that represents the mode number, E can be Young's Modulus forthe actuator 410, I can be a second moment of area for the actuator 410,ρ can be a density of the actuator 410, and A can be an area of thecross section of the actuator 410. In some examples, the mode constantcan be a function of boundary conditions, and the mode harmonic (e.g.,first mode, second mode, etc.). Boundary conditions can be how the fiberoptic scanning element is attached at its end. In some examples, theattachment can be fixed, indicating no rotation and no displacement atthe fixed end. In other examples, the attachment can be simple,indicating no displacement with rotation allowed. In other examples, theattachment can be free support, indicating both rotation anddisplacement are allowed.

In one illustrative example, the actuator natural frequency and thefiber natural frequency can each be approximately 25,000 hertz (Hz). Insuch an example, a length of the actuator 410 can be 3.903 millimeters(mm) and a length of the fiber optic scanning element 420 can be 1.970mm. Other dimensions of the actuator 410 and the fiber optic scanningelement 420 can include a piezo outer diameter (OD) (e.g., 888micrometers (μm)), piezo inner diameter (ID) (e.g., 296 μm), diameter ofthe fiber optic scanning element 420 (e.g., 125 μm), joint flexure platethickness (e.g., 70 μm) (plate is illustrated in FIG. 4C), joint flexurehub thickness (e.g., 40 μm) (hub is illustrated in FIG. 4C), and anominal excitation voltage (e.g., 100 μm). However, it should berecognized that the dimensions and attributes can be different dependingon the particular application and/or actuator.

In some examples, when the fiber optic scanning element 420 is added tothe actuator 410 to form a fiber scanning system, the natural frequencyof the fiber scanning system can be less than either the actuatornatural frequency or the fiber natural frequency. For example, thenatural frequency of the fiber scanning system can decrease with respectto the actuator natural frequency because of the added mass of the fiberoptic scanning element 420. In some examples, when the fiber opticscanning element 420 is combined with the actuator 410, the naturalfrequency of the fiber scanning system can be function of a modal massratio of the fiber optic scanning element 420 and the actuator 410. Insome examples, the modal mass ratio for the dynamic absorption designcan be 1:1, where the actuator 410 has an equal modal mass to the fiberoptic scanning element 420.

In some examples, the actuator 410 can be driven at a particularfrequency or a particular range of frequencies, which can be referred toas an operating frequency. In such examples, the actuator 410 can bedriven by a sinusoidal voltage. The operating frequency at which theactuator 410 is driven, can be such that the actuator 410 reduces itsown movement. For example, the actuator 410 can be driven at its naturalfrequency. By minimizing movement of the actuator 410, energy can bestored by the actuator 410, which can then be transferred throughreaction forces to the fiber optic scanning element 420 to gain a largeroverall deflection of the fiber optic scanning element 420. Accordingly,embodiments of the present invention in which the actuator is driven atits natural frequency to produce an increased deflection of the fiberoptic scanning element contrast sharply with conventional systems inwhich operating frequencies, particularly of tuned dynamic absorbers,differ significantly from resonant frequencies in order to reducevibration. Rather than reducing oscillation (i.e., deflection) of thefiber optic scanning element, embodiments of the present inventionincrease the range of the deflection contrary to conventional systemoperation.

FIG. 4B illustrates an example of a cross section of an alternativedesign for a fiber scanning system according to an embodiment of thepresent disclosure. The alternative design can have different naturalfrequencies for an actuator 440 and a fiber optic scanning element 450.In particular, the actuator natural frequency can be approximately50,000 Hz while the fiber natural frequency can be approximately 25,000Hz (which is half of the actuator natural frequency). In some examples,a length of the actuator in an alternative design can be 2.767 mm and alength of the fiber optic scanning element 450 can be 1.970 mm. In someexamples, the modal mass ratio for the alternative design can be 2:1,where the actuator 440 can have twice the modal mass of the fiber opticscanning element 450.

FIG. 5A illustrates an example of Bode plots for an alternative designfor a fiber scanning system according to an embodiment of the presentdisclosure. The Bode plots illustrated in FIG. 5A correlate with thealternative design of the fiber scanning system discussed in relation toFIG. 4B above in which a natural frequency of the fiber optic scanningelement is half of a natural frequency of the actuator. The Bode plotsin FIG. 5A can describe a frequency response and a phase angle forcomponents (e.g., the actuator 440 and/or the fiber optic scanningelement 450) of the fiber scanning system. In some examples, the Bodeplots can be generated using one or more linear models. However, itshould be recognized that the Bode plots may be generated using one ormore non-linear models.

In particular, a first Bode plot can graph a displacement gain for anactuator (e.g., a piezoelectric tube plot 520) and a fiber opticscanning element (e.g., a fiber plot 510) in relation to a frequencyapplied to the actuator by a voltage. In some examples, the displacementgain can be in reference to a tip of the fiber optic scanning elementand/or a tip of the actuator. In such examples, the displacement gaincan be computed using the following equation:

${{gain} = {20\; {\log \left( \frac{\delta}{1} \right)}}},$

where δ refers to a dynamic value of the fiber scanning system and the 1refers to an approximation of a static value of the fiber scanningsystem. In such examples, the static value can be normalized to 1, whichcan be an expected static deflection for the fiber scanning system. Insome examples, a static value can be a displacement of an actuator whena direct current (DC) voltage potential is applied. In such examples, aposition of the actuator may not change with time. In some examples, adynamic value can be a displacement of the actuator when an alternatingcurrent (AC) voltage potential is applied.

Referring to the first Bode plot of FIG. 5A, the fiber plot 510 canindicate that a displacement gain of a tip of the fiber optic scanningelement can increase until a frequency being applied to the actuatorreaches a natural frequency (e.g., 25,000 Hz) of the fiber opticscanning element. In some examples, the displacement gain of the fiberoptic scanning element can increase at a greater rate as the frequencyapproaches the fiber natural frequency. After the fiber plot 510 reachesthe fiber natural frequency, the displacement gain of the tip of thefiber optic scanning element can decrease (e.g., asymptotically).

The piezoelectric tube plot 520 can indicate that a displacement gain ofa tip of the actuator also increases until a frequency being applied tothe actuator reaches the fiber natural frequency. In some examples, thefrequency of the actuator can increase at a relatively linear rate on alogarithmic scale until the displacement gain of the fiber opticscanning element reaches a particular amount. Once the displacement gainof the fiber optic scanning element reaches a particular amount, moreenergy can be transferred from the actuator to the fiber optic scanningelement, causing the displacement gain of the actuator to increase at agreater rate than before the displacement gain of the fiber opticscanning element reaches the particular amount. In some examples, energytransfer from the fiber optic scanning element to the actuator is notadvantageous as the transfer of the reaction force of the fiber opticscanning element to the actuator decreases the displacement gain thatthe fiber optic scanning element can experience.

Once the frequency being applied to the actuator reaches the fibernatural frequency, the displacement gain of the actuator can drop toapproximately −10, which can equal 20 log₁₀ output/input, making theoutput/input equal to 0.31, indicating that a dynamic response is 31% ofa static response. After the displacement gain of the actuator drops,the displacement gain of the actuator can increase to a particularamount (the rate of change of the amplitude of the displacement as afunction of frequency may be dictated by an order of the linear system),and then continue to increase (at a rate similar to the rate before theparticular amount described above) until the frequency being applied tothe actuator reaches the actuator natural frequency (e.g., 50,000 Hz).After the frequency being applied to the actuator reaches the naturalfrequency of the actuator, the displacement gain of the actuator candecrease (e.g., asymptotically).

A second Bode plot can graph a phase angle for an actuator (e.g., apiezoelectric tube 540) and a fiber optic scanning element (a fiber plot530) in relation to a frequency applied to the actuator by a voltage.The phase angle can indicate a relationship between a response of theactuator and the fiber optic scanning element to a frequency input. Insome examples, the phase angle can indicate a time delay, typicallybetween a command signal and a physical response. In such examples, thephase angle can indicate the controllability of the fiber scanningsystem.

FIG. 5B illustrates an example of Bode plots for a dynamic absorptiondesign for a fiber scanning system (as illustrated in FIG. 4A abovewhere a fiber natural frequency can be approximately matched to anactuator natural frequency) according to an embodiment of the presentdisclosure. Similar to as described above for FIG. 5A, the Bode plotscan describe a frequency response and a phase angle for components(e.g., the actuator 410 and/or the fiber optic scanning element 420) ofthe fiber scanning system.

Referring to the first Bode plot of FIG. 5B, a fiber plot 550 canindicate that a displacement gain of a tip of the fiber optic scanningelement can be characterized by two peaks in the fiber plot 550. The twopeaks can represent a mode splitting that is caused by combining a fiberoptic scanning element and an actuator together into a single mechanicalsystem with both the fiber optic scanning element and the actuatorhaving the same frequency. In particular, a first resonant mode of theactuator can be associated with a first peak (sometimes referred to as afirst resonant frequency 552) formed at a frequency lower than theactuator natural frequency. In addition, a second resonant mode of thefiber optic scanning element can be associated with a second peak(sometimes referred to as a second resonant frequency 554) formed at afrequency higher than the fiber natural frequency.

In some examples, the displacement gain of the tip of the fiber opticscanning element can decrease between the first peak and the second peakas illustrated in FIG. 5B. The decrease in the displacement gain cancause the displacement gain of the tip of the fiber optic scanningelement at the fiber natural frequency to be less than either of thepeaks; however, the displacement gain, although decreased from the peakvalues, may still be higher than the displacement gain of the tip of thefiber optic scanning element of the alternative design at the fibernatural frequency (as illustrated in FIG. 5A). In some examples, adistance between the peaks in the fiber plot 550 can be a function ofthe modal mass ratio. For example, if the actuator has a larger modalmass, there can be less separation between the first peak and the secondpeak. In addition, a shape of each of the peaks can be based ondampening of the fiber scanning system. For example, one of the peakscan be higher than the other peak.

In some examples, the displacement gain of the fiber optic scanningelement can be maximized at either the first resonant frequency 552, afiber natural frequency, and/or the second resonant frequency 554. Insuch examples, the fiber scanning system can be operated at or near thepoint that is maximizing the displacement gain. In other examples, thefiber scanning system can be operated at one of the points describedabove, even if the point being operated at is not the maximum. In suchexamples, the operating point of the fiber scanning system can beselected based on a rate of change around the point. For example, thefirst resonant frequency 552 and/or the second resonant frequency 554can be unstable in terms of the displacement gain (e.g., based on anamount of change for the displacement gain in response to small changesto frequency) while the natural frequency 556 can be more stable. Insuch an example, the natural frequency 556 can be selected as theoperating point for the fiber scanning system rather than the firstresonant frequency 552 or the second resonant frequency 554.

In some embodiments, the operating point of the fiber scanning system isselected such that the displacement gain is greater than or equal to apredetermined displacement gain. In other words, during operation, thefiber scanning system can achieve a range of displacement gains bydriving the actuator at an operating frequency within a range offrequencies.

Referring to FIG. 5B, the displacement gain at the natural frequency of25 kHz is slightly greater than 40 dB, which can be referred to as thenatural displacement gain. Displacement gains greater than or equal tothe natural displacement gain can be achieved by driving the fiberscanning system at frequencies (i.e., an operating frequency) rangingfrom which is associated with the minimum frequency less than firstresonant frequency 552 at which the displacement gain equals the naturaldisplacement gain, to f₂, which is associated with the maximum frequencygreater than second resonant frequency 554 at which the displacementgain equals the natural displacement gain. Accordingly, by driving thefiber scanning system at an operating frequency in this range, adisplacement gain greater than or equal to the natural displacement gainis achieved. In some embodiments, a particular operating frequency isselected based on the natural frequency of the actuator whereas in otherembodiment, the particular operating frequency is selected based on thenatural frequency of the fiber optic scanning element.

The operating frequency can be selected such that the operatingfrequency is within a threshold of the first resonant frequency 552 orwithin a threshold of second resonant frequency. The threshold can beset such that the operating frequency is associated with a displacementgain greater than or equal to the natural displacement gain.Accordingly, as illustrated in FIG. 5B, the threshold around the firstresonant frequency could extend from frequency f₁ to 25 kHZ and thethreshold around the second resonant frequency could extend from 25 kHzto frequency f₂.

Similar to the fiber plot 550, a piezoelectric tube plot 560 can alsoinclude two resonant frequencies. In some examples, the two resonantfrequencies of the piezoelectric tube plot 560 can be located at asimilar frequency as the two resonant frequencies of the fiber plot 550.However, the displacement gain of the tip of actuator can be reduced toapproximately zero. In some examples, combined kinetic and potentialenergy of the actuator can be transferred to the fiber optic scanningelement at the actuator natural frequency, which can cause thedisplacement gain of the actuator to be reduced to approximately zero.

A second Bode plot can graph a phase angle for an actuator (e.g., apiezoelectric tube plot 520) and a fiber optic scanning element (e.g., afiber plot 510) in relation to a frequency applied to the piezoelectrictube by a voltage. In some examples, the second Bode plot can illustratethat a phase shift (e.g., a phase shift of 180 degrees) may occur ateach peak.

FIG. 5C illustrates an example of Bode plots for a comparison of adynamic absorption design and an alternative design for a fiber opticscanning element (as described above) according to an embodiment of thepresent disclosure. As can be seen, the peaks of the fiber opticscanning element for the dynamic absorber design provide the highestdisplacement gain. And while the displacement gain for the dynamicabsorber design at the point between the peaks is lower than thealternative design, this may not always be the case. In addition, evenif the dynamic absorber design has a lower displacement gain at thatpoint, the dynamic absorber design may be more stable. The idealoperating point may be determined from experimental studies.

FIG. 5D illustrates an example of Bode plots for a comparison of adynamic absorption design and an alternative design for an actuator (asdescribed above) according to an embodiment of the present disclosure.In some examples, the example can illustrate that energy is beingabsorbed from the actuator by the fiber optic scanning element in thedynamic absorption design. In such examples, a response of the actuatormay go below a static response for the dynamic absorption design.

FIG. 6 illustrates an example of a process 600 for increasing the fieldof view for a fiber scanning system.

The process 600 can include providing an actuator characterized by anactuator natural frequency of operation (610). In some examples, thefiber scanning system can include the actuator.

The process 600 can further include providing a fiber optic scanningelement coupled to the actuator (620). In some examples, the fiber opticscanning element can be characterized by a fiber natural frequency thatis determined to match the actuator natural frequency. In such examples,the fiber scanning system can further include the fiber optic scanningelement.

The process 600 can further include driving the actuator at an operatingfrequency (630). In some examples, a displacement gain of the fiberscanning system can be characterized by two split frequency peaksbounding the actuator natural frequency. In such examples, the operatingfrequency can be near the first peak of the split frequency peaks (i.e.,at a frequency within a threshold of the first peak), where the firstfrequency peak is less than the actuator natural frequency. In otherexamples, the operating frequency can be near (i.e., at a frequencywithin a threshold of the second peak), where the second frequency peakis greater than the actuator natural frequency. In other examples, theoperating frequency can be a frequency within a range between the firstfrequency peak and the second frequency peak, for example, at theactuator natural frequency. In some examples, the actuator can be drivenby a sinusoidal voltage.

A number of examples have been described. Nevertheless, it will beunderstood that various modification may be made without departing fromthe scope of this disclosure.

What is claimed is:
 1. A method for increasing a field of view of afiber scanning system, the method comprising: configuring the fiberscanning system to behave as a tuned dynamic absorber by: providing (1)an actuator characterized by an actuator natural frequency and (2) afiber optic scanning element characterized by a fiber natural frequencythat is within a threshold of the actuator natural frequency, wherein afirst displacement gain is associated with operation of the fiberscanning system at the fiber natural frequency; determining a range ofoperating frequencies, wherein the range extends from a first operatingfrequency less than the fiber natural frequency and associated with thefirst displacement gain to a second operating frequency greater than thefiber natural frequency and associated with the first displacement gain;and driving the actuator at an operating frequency within the range. 2.The method of claim 1 wherein: the operating frequency corresponds to afirst resonant frequency less than the fiber natural frequency; and adisplacement gain at the operating frequency is greater than the firstdisplacement gain.
 3. The method of claim 1 wherein: the operatingfrequency corresponds to a second resonant frequency greater than thefiber natural frequency; and a displacement gain at the operatingfrequency is greater than the first displacement gain.
 4. The method ofclaim 1 wherein: the fiber scanning system is characterized by two splitfrequency peaks, a first frequency peak having a frequency less than thefiber natural frequency and a second frequency peak having a frequencygreater than the fiber natural frequency; and the operating frequency isgreater than or equal to the first frequency peak and less than or equalto the second frequency peak.
 5. The method of claim 1 wherein the firstdisplacement gain is associated with the fiber natural frequency.
 6. Afiber scanning system comprising: an actuator characterized by anactuator natural frequency of operation; and a fiber optic scanningelement coupled to the actuator, wherein the fiber optic scanningelement is characterized by a fiber natural frequency that is configuredto match the actuator natural frequency within a threshold of theactuator natural frequency.
 7. The fiber scanning system of claim 6,wherein the actuator comprises a piezoelectric tube.
 8. The fiberscanning system of claim 6, wherein the actuator natural frequencycharacterizes the actuator when the fiber optic scanning element isseparate from the actuator.
 9. The fiber scanning system of claim 6,wherein the actuator has a cylindrical geometry having a central axis,and wherein the fiber optic scanning element passes through the actuatoralong the central axis.
 10. The fiber scanning system of claim 6,wherein the fiber optic scanning element comprises a multicore fiber.11. The fiber scanning system of claim 6, wherein the fiber opticscanning element is cantilevered.
 12. The fiber scanning system of claim6, wherein the fiber optic scanning element is coupled to the actuatorat a central position of the actuator.
 13. The fiber scanning system ofclaim 12, wherein an outside diameter of the fiber optic scanningelement at the central position is smaller than an inside diameter ofthe actuator at the central position.
 14. The fiber scanning system ofclaim 13 further comprising a retention collar surrounding and incontact with the fiber optical scanning element.
 15. The fiber scanningsystem of claim 6, wherein the fiber optic scanning element ismechanically coupled to the actuator.
 16. The fiber scanning system ofclaim 6 further comprising an intermediate element between the fiberoptic scanning element and the actuator.
 17. The fiber scanning systemof claim 6, wherein the fiber optic scanning element is coupled to theactuator in a fixed configuration, allowing no rotation and nodisplacement at a fixed end.
 18. The fiber scanning system of claim 6,wherein the fiber optic scanning element is coupled to the actuator toallow rotation of the fiber optic scanning element.
 19. The fiberscanning system of claim 18, wherein the fiber optic scanning element iscoupled to the actuator to further allows displacement of the fiberoptic scanning element.
 20. A method for increasing a field of view fora fiber scanning system, the method comprising: providing an actuatorcharacterized by an actuator natural frequency of operation, wherein thefiber scanning system includes the actuator; providing a fiber opticscanning element coupled to the actuator, wherein the fiber opticscanning element is characterized by a fiber natural frequency that isconfigured to match the actuator natural frequency within a threshold ofthe actuator natural frequency, and wherein the fiber scanning systemfurther includes the fiber optic scanning element; and driving theactuator at an operating frequency.
 21. The method of claim 20, whereina displacement gain of the fiber scanning system is characterized by twosplit frequency peaks bounding the actuator natural frequency.
 22. Themethod of claim 21, wherein the operating frequency is within athreshold of a first peak of the two split frequency peaks, and whereinthe first peak is less than the actuator natural frequency.
 23. Themethod of claim 21, wherein the operating frequency is within athreshold of a second peak of the two split frequency peaks, and whereinthe second peak is greater than the actuator natural frequency.
 24. Themethod of claim 21, wherein the operating frequency is between the twosplit frequency peaks.
 25. The method of claim 21, wherein the actuatoris driven by a sinusoidal voltage.
 26. The method of claim 20, whereinone or more attributes of the actuator are configured to cause theactuator to be characterized by the actuator natural frequency, andwherein an attribute of the one or more attributes is Young's Modulus,second moment of area, density, area of cross section, length, or a modeconstant.
 27. The method of claim 20, wherein the actuator naturalfrequency characterizes the actuator when the fiber optic scanningelement is separate from the actuator.
 28. The method of claim 20,wherein a tip of the fiber optic scanning element is configured toproject light to create an image.
 29. The method of claim 20, whereindriving the actuator causes the fiber optic scanning element to bescanned to create a set of beamlets with a plurality of angles ofincidence and points of intersection that are relayed to an eye by awaveguide.
 30. The method of claim 20, wherein driving the actuatorcauses the fiber optic scanning element to be scanned in a spiralpattern.